1. Field of the Invention
The invention relates to a leaflike shaft of a hip-joint prosthesis for anchoring in the femur, with a femur-anchoring section and a prosthesis neck.
Profiled shafts of this kind are generally known. As only a few examples in this regard reference is made to the patents EP 0 427 902 B1 or EP 0 244 610 B1 or U.S. Pat. No. 4,908,035.
As a rule the anchoring section of a shaft of the kind in question here is constructed with smooth surfaces. In EP 0 427 902 B1 it is proposed to construct one section of the shaft with contact surfaces provided with sawteeth. This measure is intended to improve fusion of the shaft to the bony substance.
It is disclosed in the patent CH-A 642 252 that the anterior and posterior leaf surfaces of the leaf part of a shaft are provided with groove-like indentations. However, bone tissue grows poorly into these. The tissue that fills up these indentations is generally a connective tissue with only slight stability.
2. Background of the Invention
The object of the present invention is to configure the femur-anchoring section of a leaflike shaft in such a way that the the tissue growing onto the prosthesis consists to the greatest possible extent of spongy bone tissue, so as to ensure long-term, firm retention of the shaft in the femur.
This object is achieved by a leaflike shaft with the characteristics given in claim 1.
The invention includes the fundamental idea that the femur-anchoring section of the shaft is substantially rectangular in cross section, so that in simplified (ignoring the tapering toward the tip) terms it is constructed as a xe2x80x9cfour-edgedxe2x80x9d profile, in particular as
oblique-cross profile
H profile
double-H or -comb profile
rectangular hollow profile
rectangular facet profile
rectangular notch profile
approximately trapezoidal profile (with or without recesses at the sides or in the interior)
or the like.
These profiles all exhibit, to a greater or lesser extent, the property that in the space between the anchoring section of the shaft and the wall of the surgically created cavity spongy bone tissue forms, so that revascularization of the bone occurs. The alternatives in accordance with the invention have the advantage that their periphery comprises substantially four edges, situated at the corners of a rectangle or trapezoid that extends perpendicular to the central axis of the shaft. This basic shape of a shaft has been found in practice to be particularly advantageous for the revascularization of the bone tissue.
It has further been found that a predetermined overdimensioning of the side surfaces of the shaft in comparison to the xe2x80x9craspedxe2x80x9d dimension (xe2x80x9cnull dimensionxe2x80x9d)xe2x80x94with the exception of the edge regions, which should fit preciselyxe2x80x94is advantageous in this respect, especially in the proximal section of the shaft.
With the further development in accordance with the invention the revascularization of the bone tissue is additionally promoted, while on one hand the necessary stability or solidity of the shaft is preserved, but on the other hand the intervening space between shaft and operation-cavity wall is enlarged, with the result that a greater amount of new spongiosa is formed.